a: \(=81\cdot51+49\cdot81=81\cdot100=8100\)

b: \(=371\left(65+25+10\right)=37100\)

a,81*51+49*153-49*72

= 81*51+49*(153-72)

=81*51+49*81

=81*(51+49)

=81*100

=8100

91 x 51 + 49 x 163 - 49 x 72

= 91 x 51 + 49 x ( 163 - 72 )

= 91 x 51 + 49 x 91

= 91 x ( 51 + 49 )

= 91 x 100

= 9100

91x51 + 49x163-49x72

=91x51+49x( 163-72)

=91x51+49x91

=91x(51+49)

=91x100

=9100

91 x 51 + 49 x 163 - 49 x 72

= 91 x 51 + 49 x ( 163 - 72 )

= 91 x 51 + 49 x 91

= 91 x ( 51 + 49 )

= 91 x 100

= 9100

`@` `\text {Ans}`

`\downarrow`

`2023 \times 14 + 2023 \times 83+97`

`= 2023 \times (14+83) + 97`

`= 2023 \times 97 + 97`

`= 196231 +97`

`= 196328`

`78 \times 31+78 \times 24+78 \times 17+78 \times 22 \times 72`

`= 78 \times (31+24+17+22 \times 72)`

`= 78 \times (31+24+17+1584)`

`= 78 \times 1656`

`= 129168`

`371 \times 69+371 \times 14+629 \times 83`

`= 371 \times (69+14) + 629 \times 83`

`= 371 \times 83 + 629 \times 83`

`= 83 \times (371+629)`

`= 83 \times 1000`

`= 83000`

`91 \times 51+49 \times 163-49 \times 72`

`= 91 \times 51 + 49 \times (163-72)`

`= 91 \times 51+49 \times 91`

`= 91 \times (51+49)`

`= 91 \times 100`

`= 9100`

`3 \times 12 \times 17 + 4 \times 9 \times 81 + 2 \times 6 \times 6`

`= 9 \times 4 \times 17 + 4 \times 9 \times 81 + 4 \times 9 \times 2`

`= 9 \times 4 \times (17+81+2)`

`= 36 \times 100` 

`= 3600`

`42 \times 17 + 58 \times 83 \times 42 \times 83 + 42 \times 83 + 17`

`= 17 \times (42+58) + 42 \times 83 \times (58 \times 83 +1)`

`= 17 \times 100 + 3486 \times 4815`

`= 1700 + 16785090`

`= 16786790`

(50+1)(50-1) = 2500 -1 = 2499 

(82-81)(82+81) = 163 

a) 51x49

=( 50+1) x(50-1)

=50x50 -1x1

=2500-1=2499

b) 82²-81²

=(82-81)x (82+81)

=1x 163

=163

Tính nhanh

51 x 49

b) 82² - 81²

a) 51x49

=( 50+1) x(50-1)

=50x50 -1x1

=2500-1=2499

b) 82²-81²

=(82-81)x (82+81)

=1x 163

=163

   35 \(\times\) 49 + 51 \(\times\) 36

= 35 \(\times\) 49 + 51 \(\)\(\times\) (35 + 1)

= 35 \(\times\) 49 + 35 \(\times\) 51 + 51

= (35 \(\times\) 49 + 35 \(\times\) 51) + 51

= 35 \(\times\)( 49 + 51) + 51

= 35 \(\times\) 100 + 51

= 3500 + 51

= 3551

Số số hạng của S₁:

(51 - 1) : 2 + 1 = 26 (số)

Số số hạng của S₂:

(153 - 47) : 2 + 1 = 54 (số)

S₁ = (51 + 1) . 26 : 2 = 676

S₂ = -(153 + 47) . 54 : 2 = -5400

⇒ S₁ + S₂ = 676 + (-5400) = -4724

35 x 49 + 51 x 36 = 35 x 49 + 51 x ( 35+1) =35 x 49 + 51 x 35 + 51 = 35 x ( 49 + 51 ) + 51 = 35 x 100 + 51 = 3500+51 = 3551

=(36-1)x49+51x36

=36x49-1x49+51x36

=36x49-49+51x36

=36x(49+51)-49

=36x100-49

=3600-49

=3551

Tính nhanh 9106×101-9136

-25 x 72 + 25 x 21 - 49 x 25

= 25 x (-72 + 21 - 49)

= 25 x (-100) 

= -2500

-25 x 72 + 25 x 21 - 49 x 25

= 25 x ( -72 ) + 25 x 21 - 49 x 25

= 25 x ( -72 + 21 - 49 )

= 25 x ( - 100 )

= -2500

-25 x 72 + 25 x 21 - 49 x 25

= 25 x (-72 + 21 - 49)

= 25 x (-100)

= -2500

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